1. Technical Field
The present invention generally relates to a system to monitor particle contamination in semiconductor manufacturing facilities. More particularly, the present invention generally relates to a particle monitoring system capable of automatically detecting the level of polymer deposited on inner walls of a process chamber.
A claim is made to Korean Patent Application No. 2004-63, filed on Jan. 2, 2004, the disclosure of which is hereby incorporated by reference.
2. Discussion of the Related Art
Conventional semiconductor manufacturing techniques, such as dry plasma etching, reactive ion etching, and ion milling, have developed to overcome various limitations associated with a chemical etching technique. In the dry plasma etching, the vertical etching speed is much faster than its horizontal etching speed, such that an aspect ratio can be properly adjusted. In fact, a fine feature with a high aspect ratio can be formed on a thin film having a thickness greater than 1 μm using the dry plasma etching technique.
In a process chamber under pressure, energy is added to ionize a reactive gas to thereby form plasma. Atoms having an electrical charge are attracted to a wafer having an electrical potential. The atoms collide with the wafer in a vertical direction, and areas on the wafer unprotected by a mask are removed.
The etching process is effectively implemented by utilizing a chemically reactive gas that targets a specific material. The reactive ion etching technique combines the strong etching effects of both dry plasma etching and chemical etching techniques. It is conventionally known that chemically reactive agents cause excessive electrode wear.
Preferably, plasma is uniformly distributed across the surface of a wafer to achieve a uniform etching speed over the entire surface of the wafer. For example, U.S. Pat. Nos. 4,595,484, 4,792,378, 4,820,371, and 4,960,488 generally disclose a conventional showerhead electrode to distribute gas through a plurality of holes formed on the electrode. The patents also generally disclose a gas distribution plate having a plurality of rows of apertures to provide a uniform flow of gas vapor to a semiconductor wafer.
A conventional reactive ion etching system generally includes an etching chamber having an upper electrode (anode) and a lower electrode (cathode) disposed therein. The cathode applies a negative bias to the anode and the etching chamber walls. A mask covered wafer is directly laid on the cathode. A reactive gas, such as CF4, CHF3, CCIF3, SF6, or a mixture thereof is supplied together with O2, N2, He or Ar gas into the etching chamber. The etching chamber is maintained at a pressure of a few millitorr. The upper electrode is provided with a plurality of gas holes to uniformly distribute the gases in the etching chamber. An electric field applied between the anode and the cathode dissociates the reactive gas to form the plasma. The surface of the wafer is etched by a chemical reaction with the reactive ions, and a momentum transfer of ions colliding against the surface of the wafer. The electric field created by the electrodes attracts ions toward the cathode, such that the ions are guided to vertically collide against the surface of the wafer.
Therefore, this process can produce a well-defined vertically etched side wall.
In another conventional etching process, a vacuum processing chamber is supplied with an etching gas or a deposition gas. The gas is activated into a plasma state by applying an RF field to implement etching, and then a chemical vapor deposition (CVD) process is carried out on a substrate. U.S. Pat. Nos. 4,340,462, 4,948,458, 5,200,232, and 5,820,723 generally disclose a parallel plate transformer coupled plasma (TCPTM) (referred to as inductively coupled plasma (ICP)), an electron-cyclotron reactor, and components thereof. The components preferably have high anti-corrosion properties, because the reactor must be resistant to corrosion caused by the plasma atmosphere, and contamination by particles and/or heavy metals.
Inner walls of a plasma reactor are generally made of aluminum or aluminum alloy. Several techniques for coating the inner walls with various coating materials have been proposed to prevent the corrosion of the inner walls. For example, U.S. Pat. No. 5,641,375 generally discloses an anodized aluminum chamber to reduce plasma corrosion and wear of the inner walls. However, once the anodized layer wears off, the chamber itself must be replaced.
U.S. Pat. No. 4,491,496 generally discloses a technique of flame spraying Al2O3 on a metallic surface of an etching chamber. U.S. Pat. No. 5,680,013 teaches that a ceramic coating usually cracks due to the thermal coefficient of expansion mismatch between aluminum and the ceramic coating, resulting in the deterioration of the exposed aluminum by the plasma species. U.S. Pat. No. 5,085,727 discloses a plasma chamber having a carbon coated inner wall, in which the coating is deposited by plasma assisted CVD.
U.S. Pat. Nos. 5,366,585, 5,556,501, 5,788,799, 5,798,016, and 5,885,356 generally disclose a liner arrangement to protect an inner wall of a plasma chamber. For example, U.S. Pat. No. 5,366,585 discloses a free standing ceramic material machined from solid alumina and having a thickness of at least 0.005 inches. A ceramic layer is deposited without consuming the underlying aluminum.
U.S. Pat. No. 5,556,501 discloses a process-compatible liner made of polymer, quartz or ceramic. U.S. Pat. No. 5,788,799 discloses a temperature-controlled ceramic liner having a resistance heater. The ceramic comprises oxides of alumina, silica, titania, and zirconia; carbides such as silicon carbide, titanium carbide, and zirconium carbide; and nitrides such as aluminum nitride, boron nitride, silicon nitride and titanium nitride. U.S. Pat. No. 5,798,016 discloses a liner for an etching chamber made of ceramics, aluminum, steel and/or quartz. Aluminum is a preferred material because it is easy to machine. Preferably, the lining is coated with Al2O3, Sc2O3, or Y2O3 to protect the aluminum against the plasma. U.S. Pat. No. 5,885,356 discloses a wafer pedestal comprised of a ceramic liner of alumina and a ceramic shield of aluminum nitride. U.S. Pat. No. 5,904,778 discloses a chamber wall, a chamber roof, or a collar around a wafer coated with a free standing silicon carbide substrate by a CVD process. U.S. Pat. No. 5,292,399 discloses a wafer pedestal enclosed with a SiC ring. U.S. Pat. No. 5,182,059 discloses a technique of producing SiC sintered material.
Various materials for use as plasma reactor components (e.g., the showerhead gas distributing system) have been proposed. For example, U.S. Pat. No. 5,569,356 discloses a showerhead made of silicon, graphite or silicon carbide. U.S. Pat. No. 5,888,957 discloses a showerhead made of amorphous silicon, SiC or Al. U.S. Pat. Nos. 5,006,220 and 5,022,979 disclose coating a showerhead electrode with SiC by a CVD process to provide a surface thereof with highly pure SiC.
However, a technique to improve the substance and/or coating used as plasma reactor components, in view of the demand for highly pure and anti-corrosive components for semiconductor processing facilities is required. In addition, it is useful for a chamber material to utilize a substance capable of extending the service life of the plasma reactor, and thus reducing the down time and process costs.
In a conventional dry etching chamber, a semiconductor wafer is etched by plasma gas and RF power. However, the wafer may be damaged by byproduct (polymer) particles during the etching process. According to the conventional method of cleaning the dry etching chamber, the etching chamber is periodically cleaned to remove the polymer particles. The polymer particles usually deposit on the inner walls of the process chamber, but due to leakages, regardless of process management (PM) schedules, a high number of particles are produced, which adversely affect process yields. In order to solve the above problem, the level of the polymer particles must be monitored, and the etching chamber cleaned accordingly. The conventional method of monitoring and identifying the level of polymer particles consumes a lot of time which lowers productivity.